This invention relates to a novel class of cephalosporin antibiotics. In particular it relates to 3-halo cephalosporins represented by the following generalized formula ##STR1## wherein R is hydrogen or an acyl group derived from a carboxylic acid, R.sub.1 is hydrogen, a carboxylic acid protecting ester group or a pharmaceutically acceptable ester or salt, and X represents fluoro, chloro, bromo, or iodo.
The compounds of the invention possess the unique structural characteric of a halogen atom directly bonded to the carbon atom in the 3-position of the dihydrothiazine ring. According to the cepham nomenclature system the above depicted compounds are named as 7-amino- or 7-acylamido-3-halo-3-cephem-4-carboxylic acids, salts and esters.
Prior to this invention 3-bromomethyl-3-cephem-4-carboxylic acid esters, U.S. Pat. Nos. 3,647,788 and 3,688,203, and 3-bromomethyl-2-cephem-4-carboxylic acid esters, U.S. Pat. No. 3,637,678 were described. These known 3-bromomethyl compounds are described as useful intermediates for preparing cephalosporin antibiotics. In contrast with these intermediates, the 3-halo-3-cephem-4-carboxylic acids described herein are especially valuable antibiotics.